This invention relates to the recovery of bacitracin. In a particular aspect, this invention relates to a process for the recovery of bacitracin from a fermented beer containing it.
Bacitracin is a valuable antibiotic for topical use in the practice of medicine or as a growth promoter in animal feed supplements. The zinc salt of bacitracin is especially valuable in these uses because it is exceptionally stable over long periods of time.
The antibiotic bacitracin is produced by cultivating strains of bacteria of the Bacillus subtilis or Bacillus licheniformis groups in a suitable liquid nutrient fermentation medium. The bacitracin in the fermentation medium is present in dissolved form only in small quantities, i.e. on the order of about 300-600 units per milliliter. The separation and recovery of this small amount of material from a large volume of medium having complex character presents numerous difficulties.
Generally, a bacitracin containing solution is recovered from the fermented beer by the use of vacuum rotary drum filtration. In this procedure a filter aid such as diatomaceous earth is added to the fermented beer. The pH is then adjusted with strong acid into the range of about 3.0-3.5. The resulting material is filtered over a rotary drum filter precoated with an appropriate thickness of the same filter aid. The filtrate recovered is pH adjusted to neutrality and filtered again through a filter such as a plate and frame press to remove further impurities and filter aid particles. This filtrate is then passed to the solvent extraction step. This method can account for an 18-33% loss of the initial bacitracin. Bacitracin is lost in the pH adjusting steps due to the shock of the sudden pH shifts and is also lost in the waste filter aid. This procedure produces a cloudy filtrate to be extracted. The used filter aid also poses a solid waste disposal problem.
In the past, various procedures have been employed for recovering bacitracin from solutions containing bacitracin. One such procedure involves filtering the fermentation medium to remove solid materials, extracting the resulting filtrate containing the bacitracin with a suitable solvent for bacitracin, for example, a lower aliphatic alcohol, to form a solution of bacitracin in the alcohol, adding water to the solution, and adjusting the pH of the solution downward to less than 4.0 by addition of an acid to form a solution of bacitracin in the water. The bacitracin is then recovered from the water by suitable means, such as spray drying or freeze drying. For example, it is known from Senkus et al., U.S. Pat. No. 2,609,324 to recover bacitracin from a filtered, fermented beer containing it by extracting with butanol, extracting the bacitracin from butanol with an aqueous solution of phosphoric acid at pH 2.0, followed by a second extraction with butanol to free the bacitracin from phosphoric acid. Water was added and the butanol was then evaporated, leaving the bacitracin in aqueous solution from which it could be easily recovered by freeze drying. This process was subsequently modified to adjust the pH by treatment of the aqueous acid extract to eliminate impurities and improve the color, and the second butanol extract was also subjected to treatment designed to improve the yield. After evaporating the butanol, the bacitracin was precipitated from the aqueous solution by mixing with a solution of a zinc salt as disclosed by Zinn et al., U.S. Pat. No. 2,834,711. The precipitate was then separated and dried. Alternatively, it is known to recover the bacitracin by dehydrating the aqueous bacitracin solution by the process known as freeze drying.
Another procedure for separating bacitracin from a fermentation beer containing it is to filter the fermentation beer to remove large impurities then to sorb the bacitracin from the filtrate on a carboxylic acid type ion exchange resin. The bacitracin is eluted from the exchange resin with a weak base and recovered from the eluate by evaporation. Such a method is taught by Hodge et al. in U.S. Pat. No. 3,891,615 which employs such an ion exchange resin.
Previously employed procedures for the recovery of bacitracin including the procedures described above possess many disadvantages. The principal disadvantage is the loss of a substantial portion of the bacitracin during recovery. The primary effort of designing improvements for the recovery of bacitracin has been to develop improvements in the extraction process. Such as shown by Miescher, U.S. Pat. No. 3,795,663. There has been a long-existent need for an improved process that would further increase the recovery of bacitracin from a fermented beer over the known methods of recovery.
The prior art of which Applicants are aware is recited above in the specification and includes the following U.S. Pats.: Senkus et al., U.S. Pat. No. 2,609,324; Zinn et al., U.S. Pat. No. 2,834,711; Hodge et al., U.S. Pat. No. 3,891,615; and Miescher, U.S. Pat. No. 3,795,663. These references do not anticipate nor make obvious the process hereinafter disclosed. The reference of Senkus teaches a method of recovery of bacitracin by the extraction of the fermentor beer with butanol. The reference of Zinn discloses a method of recovery by precipitating the bacitracin from an aqueous solution by the addition of a zinc salt. The reference of Hodge discloses a method of recovery of bacitracin as the calcium or magnesium complex of an alkylbenzenesulfonic acid. All of these references describe methods of recovering the bacitracin. The references do not disclose, as does the invention described herein, how to increase the amount of bacitracin in solution from which it is to be recovered. The invention herein disclosed is for a process that precedes the recovery steps described in the above-named references. The methods of recovery described in the above references can be used in combination with the process of this invention.